October 14, 2010

Salmon Genetic Characteristics Being Lost Due To Climate Change

A study has found that the distinct genetic characteristics of salmon populations in Spain are dwindling because of climate change and human interference.

The researchers from the universities of Exeter, UK, and Oviedo, Spain said that disrupting the species' migratory behavior and strong homing instinct could have long-term consequences.

They also said that they were trying to find a way to "disentangle" the individual threats affecting salmon populations.

The study focused on the changes from data taken over a 20-year period to Atlantic salmon populations in Asturias, Spain.

"Salmon develop quite distinct population structures because of their ability to home to their natal rivers," co-author Jamie Stevens, from the University of Exeter's School of Biosciences, told BBC News.

"If you have such a defined system, they will quite quickly develop genetic profiles that become definitive to a particular river system."

He said the unique characteristics meant that the fish adapted to the conditions found within a particular river.

"There is a whole bunch of things: river chemistry, ability of the fish to withstand things like temperature, behavioral factors like run time to the sea and return time to spawning grounds," said Stevens.

"The reason why we do not want those structures broken down is because we know that those local populations have a range of adaptations that can give the fish an advantage within that river."

The team studied 924 tissue samples from adult fish returning to five rivers in Asturias between 1988 and 2007. They discovered that the results were consistent with high levels of mixing between local populations of salmon.

Stevens said the study identified two distinct periods. There were a lot of "foreign" fish being introduced to the river systems up until 1992. After this period, the practice was stopped, but there still remained a high number of "straying fish."

"Historically, people who like fishing like to have big fish coming up their rivers, so there has been human movement of fish, such as from highly productive rivers in Scotland to other areas," he told BBC.

"Introduced fish would, typically, be chosen for larger sizes and faster growth rates but they may have had very poor survival rates at sea or poor at returning to the river or spawning."

"That stopped in 1992, but we still had problems. As our paper shows, there is still not a big recovery towards the genetic differences that is a signal of healthy populations."

"So as the impact from the movement of fish by humans is subsiding, we have got other things coming into play that are also causing disruptions."

Previous studies found that increased water temperatures was linked to an increase in fish straying between rivers and a breakdown of population structures.

"Increased water temperature appears to disrupt the fidelity of salmon returning to their natal rivers," Stevens added.

The team attempted to untangle how the different factors were undermining the salmon population structures of the five rivers.

They suggested that while the impact of the introduction of foreign fish was decreasing over time, the influence of changes to water temperature was becoming increasingly important.

They said that more studies needed to be done in order to obtain a clearer picture.

"Without many additional studies, it is not possible to determine the exact moment or life stage when the population structuring was eroded," they wrote.

"Long datasets of well-monitored populations could serve for this purpose."

They added: "The ability to disentangle the effects of climatic changes and anthropogenic factors (fisheries management practices) is essential for effective long-term conservation of this iconic species."

Stevens also told BBC that salmon was often used as an indicator for the state of rivers: "Monitoring a fish that is a top predator gives you a really good feel for the overall health of river systems that you might want to manage."

The team reported their findings in the journal Global Change Biology.